This invention relates to a method for treatment in the form of scale removal from, or application of coating to, internal surfaces in a closed fluid system A,B, such as pipes and tanks, by the use of a two- or multiphased flow being brought through the fluid system. The invention also relates to an apparatus for treatment in the form of scale removal from, or application of coating to, internal surfaces in a closed fluid system A,B, such as pipes and tanks, by the use of a two- or multiphased flow being brought through the fluid system.
Industrializing has entailed use of vast amounts of chemicals and solvents for various applications. In spite of improvements of the industrial processes and increasingly stricter standards for process cleanliness, the environment is exposed to substances that are toxic and harmful to the environment. These substanses are often very stable and only slowly decompose, if they decompose at all.
A reason for this is the use of chemicals and solvents in the industry for scale removal . In the industry there is a need for reasonable solutions entailing short shut down periods, and this often leads to use of chemical cleaning methods. The result is release of substances that are harmful to the environment.
Below various types of scale are described where chemicals and solvents frequently are utilised for scale removal:
Algae growth and other organic deposits, e.g. in pipe networks supplying water for consumption, fire-fighting facilities and process water. Pipe networks can have major dimensions, e.g. in water mains from reservoirs to cities, and smaller dimensions such as in buildings and ships.
Percipitation deposits of cabonates, phosphates or other chemical compounds that over time may precipitate from a fluid flow.
Sedimentation deposits of organic compounds such as oil, kerosene, fat and vax deposits in pipelines.
Corrotion deposits arising with oxidation over time, such as on inner surfaces in pipe systems and tanks.
Heavy-duty scale removal is to a great extent done by jet water washing and the use of a host of chemical sovents, also combined with high fluid temperatures.
Current knowledge about, and use of, chemicals and solvents is to some extent advanced high technology. The practical implementation of the methods and procedures using such agents are relatively less advanced, leading to major waste, danger of releasing these agents into the environment and of injury to personnel.
Because time reductions and cost savings are important factors for achieving the set goals, inadequate control of the properties of chemicals being present in a process activity have had to be accepted. Unstable temperatures may cause toxic-vapours and fast-corroding reactions. The concentrations of the cleaning fluid must be controlled at all times in order to achieve the intended effects and to avoid wasting chemicals. It must be possible to carry out quality checks on, e.g., work, hours and other factors of interest, both during the process and/or after completion.
Jet water washing for cleaning the inner walls of pipes calls for a high fluid velocity in the internal volume of the pipe. The same effect is achieved at lower pressure through the use of a standard two-phase flow in pipes by injecting air or another gas into the liquid flow, increasing the liquid velocity along the pipe wall.
The following is cited from patent literature: In EP 0 490 117 A1 a method is described for cleaning a pipeline with the aid of a two-phased flow based on liquid and gas, achieving an internal annular flow through the pipe, dependent on the density, surface tension, viscosity and given velocity on the fluid. The method specifies a gas/liquid mix ratio in the order of 3,000 to 7,500 m3: 1 m3 or in the order of 2.0 to 6.0 kg:1 kg.
The apparatus for carrying out the method comprises a source of pressurized gas adapted for blowing the gas flow through a pipeline also being connected to a source of liquid, the source of pressurized gas being dimensioned and formed for generating a two-phase flow.
There is through this invention developed a method for treatment in the form of scale removal from, or application of coating to, internal surfaces in a closed fluid system, such as pipes and tanks, by the use of a two- or multi-phase fluid flow being brought through the fluid system. The novel and inventive features are that the fluid flow is composed of liquid and gas with a substantially higher volume of gas than of liquid, being that liquid and gas in a quantity-controlled ratio and at a given pressure are supplied to a mixing head, the outlet of which is connected to an inlet to the fluid system, while an outlet from the fluid system leads to an expansion separator, that liquid and gas exit separately from the expansion separator, that the gas from the expansion separator is brought with the aid of a pump to the mixing head, that the liquid, possibly containing solid substances or particles from the expansion separator, is filtered to separate. unwanted components from the liquid, and that at least a part of the liquid is recycled to the mixing head, preferably with the aid of a pump.
For carrying out the method according to the invention, an apparatus is developed, comprising a mixing head with quantity-controlled inlets for gas and liquid, respectively, and an outlet which is adapted to be connected to an inlet to the fluid system, an expansion separator with the inlet being adapted to be connected to an outlet from the fluid system, separate outlets for gas and liquid, respectively, with possible content of solids or particles from the expansion separator, a pump for transferring the gas from the expansion separator to the gas inlet on the mixing head, a filter unit connected to the liquid outlet from the expansion separator, a valve arrangement connected to the liquid oultet from the expansion separator by means or mixing head, the filter unit, and an outlet for dumping non-reusable liquid or possibly solids or particles, and a supply line for new liquid, in that recycling of liquid to the mixing head is done preferably with the aid of a pump.
In this invention equipment can be cleaned by means of a two-phase fluid flow at relatively low pressure. Low flow pressure leads to reduction of leakages to the environment and allows for recycling of liquid and gas separately.
The invention will be described in further detail below, with reference to the attached drawings.